User interfaces which enable multimodal access to applications have become increasingly popular in the area of human-computer-interaction. A modality is typically defined as a path of communication between a human and a computer, and where a single device may include one or more modalities.
Multiple input devices which do not individually support multiple modalities may be federated to allow user interaction with multimodal-enabled applications, beyond those levels of interaction offered by a traditional keyboard, mouse, pen or display. Multimodal access initiatives have been developed, for example, by the WORLD WIDE WEB CONSORTIUM® (“W3C®”) Multimodal Interaction (“MMI”) Activity Working Group. See, e.g., ABOUT W3C: ACTIVITIES. 
Although many applications include user interfaces which are designed to be accessed via one particular device, it has also become increasingly popular to design applications which utilize split user interfaces for display on disparate devices. Using split user interfaces, independent modalities are essentially combined for the purpose of accessing a single application, resulting in a user interface which may distributed across many devices. Traditionally, a user interface is split by either dividing the user interface in parts and displaying each part on a device best suited for a desired modality, or by replicating the same user interface on every device.
Using split or replicated user interfaces, significant disadvantages arise if all user interface portions are not simultaneously refreshed in response to a user input. In particular, if the user inputs a command to the application which requires that all distributed user interface portions be synchronously refreshed, the user may suffer from confusion if the disparate modalities do not refresh at the same time.
The MMI Activity Working Group recommends the use of Synchronized Multimedia Integration Language (“SMIL”), which attempts to synchronize multiple output streams by defining ‘begin,’ ‘end,’ and ‘duration’ times for various events. In one brief example, if a video is played using a <VIDEO BEGIN=“1S” DUR=“5S” . . . /> command, the video starts one second after the relative start time of a parent element. These times are merely relative to other times, although they are initially related to a SMIL presentation start time.